In the past, a thermoplastic resin has caused insufficient transferability at high temperature and high humidity, and tended to generate uneven gray scale images such as a halftone and so forth, caused by scratches generated in an electrophotographic photoreceptor. In order to solve this problem, a protective layer is provided on the electrophotographic photoreceptor, and studies on the layer surface hardness of the electrophotographic photoreceptor increased and strengthened via crosslinking reaction have been done (refer to Patent document 1, for example).
The electrical resistivity of this protective layer in which metal oxide is dispersed is tried to be controlled, and a suitable volume resistance of 1×109-1×1015 Ω·cm has been disclosed (refer to Patent document 2, for example).
However, there was a problem such that unevenness of a coated layer was generated when a coating solution into which a large amount of metal oxide was added was coated to control electrical resistivity with the electrical resistivity of the protective layer depending on the addition amount of metal oxide. There was also a problem such that mechanical strength of the protective layer was lowered when the addition amount of metal oxide was reduced. Further, there was another problem such that the metal oxide shortened life of the coating solution via its sedimentation in the case of insufficient dispersibility of the metal oxide, resulting in a decline of productivity, and incident light scattering caused by dispersed particles was produced during formation of the coated layer. Thus, the protective layer in which metal oxide is dispersed produces a problem such that electrical resistivity and mechanical strength are satisfactory, but defects of the coated layer caused by dispersion failure, and light scattering are generated. No method to totally satisfy the foregoing has not yet been found in the current situation.
(Patent Document 1) Japanese Patent O.P.I. Publication No. 10-312139
(Patent Document 2) Japanese Patent O.P.I. Publication No. 11-202530